Interlocked metal seam structure with in-plane stabilization

ABSTRACT

A formed metal ring, made from a strip of material which has a tongue at one end and a groove at the other. The tongue and groove are interdigitaled to form a seam, and abut each other with an interference at their edges. The interference is made by flattening a dimple into the plane of the material so as to move the material of one edge into interference with the other edge. The ring has a perimeter pattern in its surface containing the shapes resulting from the flattening of the dimple.

CROSS-REFERENCE TO OTHER APPLICATION

This is a division of applicant's co-pending U.S. patent applicationSer. No. 256,718, filed Apr. 23, 1981, now U.S. Pat. No. 4,383,354 whosetitle at the time of filing was "Interlocked Metal Seam Structure WithIn-Plane Stabilization".

FIELD OF THE INVENTION

This invention relates to the formation of interlocked metal seams instructures such as rings formed from sheet, plate, or strip stock to aring structure.

BACKGROUND OF THE INVENTION

Interlocking joints in rings, cylinders, and other tubular structuresare customarily assembled during or after the primary fabrication of thecylinder itself. Tangential forces tending toward in-plane separation ofthe joint are resisted by the interlocking geometry of the jointstructure itself or by friction in simple tongue and groove structures.That is to say, this structure resists the direct pulling apart of thejoint edges, and of course also any lateral in-plane movement. Inaddition, friction between the interlocked edges of the joint, alongwith the stiffness of the total structure, provides resistance againstradial or out-of-plane displacement of the interlocked joint ends, eventhough there is no basic joint geometry which prohibits the out-of-planedislodgement of the joint. This is to say, these frictional forces tendto discourage one seam edge from "popping out" relative to the other.

In thin wall structures, particularly those having a largediameter-to-thickness ratio, the joint friction and the structuralstiffness are sometimes insufficient effectively to resist out-of-planedislodgements of the joint when the structure encounters impact orcrushing loads during transit or use. Also these out-of-plane jointdislodgement problems can further be aggravated by cut edges of thejoint which are off-square, due to normal sheared edge geometries or dueto breakdown of the edge corner during the engagement of theinterlocking joint. These undesirable conditions further reduce theholding friction, and sometimes even provide a preferred direction ofradial displacement ("dislodgement") under shock or crushing loads.

It is an object of this invention to provide means for strengthening thejoint, particularly against radial or out-of-plane joint rupture,whereby a joint can be manufactured in an expedient and inexpensiverolling and stamping operation and with positive restraints in all threeaxes of movement relative to the plane in which the seam is formed.

BRIEF DESCRIPTION OF THE INVENTION

In this invention, a piece of metal has tongues and recesses, and isformed into a cylinder so the tongues engage in the recesses. An area ofthe metal at or adjacent to an edge of a tongue or recess is movedout-of-plane to form all or part of a dimple-like structure ("dimple").After engagement of the tongues and recesses, the dimple is flattened,and its material is returned to the plane in a motion which includes atleast some lateral movement of the metal. This causes the edges of thetongue and recess to be brought into a firm abutment, which providesin-plane reinforcement.

The dimple may be formed before or after the tongues and recesses areformed, or after the tongues and recesses are interengaged.

According to a preferred but optional feature of this invention thedimple is formed in the material before the tongues and recesses arecut, and at a spacing from where the edge of the material will be whenit is cut.

The above and other features of this invention will be fully understoodfrom the following detailed description and the accompanying drawings,in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a completed ring according to the invention;

FIG. 2 is an end view of FIG. 1;

FIG. 3 is a fragmentary plan view of a tongue with a dimple in it beforeflattening of the dimple;

FIG. 4 is a cross-section taken at line 4--4 in FIG. 3;

FIG. 5 shows the process of flattening the dimple of FIG. 3;

FIG. 6 is a fragmentary cross-section taken at line 6--6 in FIG. 1;

FIG. 7 is a fragmentary enlarged plan view taken at line 7--7 in FIG. 6;

FIG. 8 shows an intermediate step in an alternative process for makingthe ring;

FIGS. 9 and 10 are fragmentary plan views of other useful tongue,recess, and dimple constructions;

FIGS. 11, 13 and 15 are fragmentary plan views of other relationshipsbetween the dimple and a related edge of material; and

FIGS. 12, 14 and 16 are cross-sections taken respectively at lines12--12, 14--14 and 16--16 in FIGS. 11, 13 and 15.

DETAILED DESCRIPTION OF THE DRAWINGS

In FIG. 1 there is shown a formed metal cylinder 10. The example givenis a metal cylinder having a wall thickness of approximately 1/8", adiameter of approximately 21/2" and a length of approximately 3". It issuitable for the stator ring of a conventional electric motor, and canconveniently be made of low carbon steel. Such steel is customarilyobtained in plate, strip, or coil form, and in this invention it isformed to a cylinder.

The object of this invention is to provide an improved seam 15 whichwill more securely hold the ring in its assembled condition, and inparticular give support to the edges of the seam against dislodgementout of its plane.

For purposes of this invention, "the plane" referred to is that ofFIG. 1. One direction (or axis) of reinforcement is horizontally in FIG.1 parallel to axis 16 of the ring (axial reinforcement). The other isperpendicular to the seam in the plane (tangential reinforcement), andresistance along these directions is provided by the geometry of theseam itself.

The seam has one or more tongues 17 and recesses 18. It will be noticedthat these are frequently complementary to one another so that a tonguecan enter and interengage in a respective recess. In fact, the same diefrequently will have sheared both ends of the metal which will be formedto make the ring. A customary cut-off die with appropriate contour issuitable for this purpose. The tongues and recesses are usually designedto resist both tangential and axial in-plane joint displacement.

Another direction (axis) of separation is out-of-plane, i.e., radiallyapart normal to the plane, and may also be thought of as a radial orout-of-plane separation. This type of separation is normally resisted bythe frictional forces exerted on the abutting boundaries of the tonguesand recesses and by the inherent tendency of the ring to retain itsformed shape. Of course there may be some tendency of the ring materialto spring back, and this is principally resisted in prior artconstructions by the friction. It follows that increasing the frictionis beneficial to retention of the ring shape and stabilization of theseam. Any means which can cause an action reinforcing the in-planestability and resisting out-of-plane dislodgement is to be desired, andthat is provided by means of this invention.

In order to accomplish this invention, dimple-like structures("dimples") are formed in local regions of the metal. Their generalshape is best shown in FIGS. 3 and 4. For longer seam edges, the dimplesare preferably lozenge-shaped and alongside or near some relativelystraight edge portion of a tongue or recess.

The dimples, however shaped, constitute local regions of metal whichhave been moved out-of-plane. An ultimate objective is to attainenhanced frictional and in-plane locking engagement along a substantiallength of material, and therefore the shape and location of the dimpleswill be selected in accordance with the effect desired as dictated bythe shape of the tongue or recess. As will later be shown, shapes otherthan lozenges can be used, for example circular, dome-shaped dimples.

It will be noted here that both edges (i.e. abutting ends of the bentstrip) may be considered as having tongues and recesses, or there may beonly one of either on a respective edge, depending on the geometry (andon the terminology). The shapes are complementary, and a portion whichenters a recess in the other part is for convenience referred to as atongue. In order to provide for best retention, a re-entrant shape oftongue and recess is preferably provided. This is to say that a pair ofrecess edges such as edges 22, 23 are formed which are abutted by tongueedges 24, 25 respectively. These form a key-type engagement to restrainagainst axial and tangential in-plane forces at the seam edge.

The presently preferred technique for forming the dimples is to formthem before the material is slit to make the tongues and grooves.Because the desired locality of the dimples is known, and the localitywill later be discussed in detail, they can with this preferredtechnique be formed at any time prior to the actual shearing of thestock to form the edges. This has the advantage that, when the tonguesand recesses are interengaged there is an initial nearly net fit allalong the edge of the seam. When the dimple is flattened out, then themetal which will be displaced sidewardly will make an appreciablytighter "interference" type fit with the edge that it abuts.

It is also possible to form the tongues and grooves before forming thedimples and even to form the cylinder and interengage the tongues andrecesses before forming the dimples, and the consequences of so doingwill later be discussed.

The terms "cylinder", "ring" and "tube" are used interchangeably herein.The term "flattening" as used for the dimples is used in a sense ofcoining or ironing of the joint assembly. This will customarily beaccomplished by the final forming load in a conventional press or othermetal forming machine.

The preferred shape of dimple 30 is shown in FIGS. 1, 3 and 4. It islozenge-shaped with a somewhat flattened bottom 31 on the concave side,and with a generally loaf-shaped surface 32 on the convex side. Asubstantial area of metal is moved out-of-plane i.e., it is shifted awayfrom the face of the metal. In consequence, the metal is somewhatthinned, and it also is drawn to form a longer "path" from edge to edgeas shown by arrow 33 in FIG. 4. The metal along this path has inherentstiffness, and also is bent.

When the seam is to be completed, then as shown in FIG. 5, a pair offorming bodies 35, 36 are brought against the faces to compress thedimple back into plane. This causes force fields as shown by arrows 37,38 and 39. Force 37 causes some crushing action to return the metal tothe plane. Force 38 causes lateral movement at the tongue edges. Force39 causes a lifting torque at the edge.

The consequences of forces 37, 38 and 39 are best shown in FIGS. 6 and7. Edge walls 40 and 41 have been forced together very strongly.Surfaces 31 and 32 have been generally flattened, and are surrounded byring-like depressions 42, 43. Of course the dimpled material neverreturns precisely to where it was drawn from, and the redistribution ofmaterial has important consequences. For example, note in FIG. 6 thecurvatures 47, 48 at the edges of walls 40 and 41. This reshaping of theedge walls is the consequence of forces 38 and 39, and provides a typeof "key-lock" against edge displacement which adds to the frictionaleffect in resisting radial out-of-plane separation. This "key-lock"effect is achieved by forcing the dimpled edge into the characteristicnon-square geometry of the other cut metal edge.

When the dimple is formed before the tongues and recesses are cut, therewill be an initial net fit of the tongue and recess when the joint isassembled, and the displacement of the metal when the dimple isflattened will add interference to the existing net fit. This gives thebest results, but is not a limitation on the invention. For example,FIG. 8 shows in a schematic and exaggerated way an intermediatecondition when the dimple is formed after the tongues and recesses areformed, either before or after the ring is formed and the tongues andrecesses are interengaged.

In FIG. 8, tongue 50 is shown interengaged in recess 51. Dimples 52, 53have been formed after the tongues and recesses were formed. The resultis a slight "drawing back" of material at tongue edges 54, 55 so as toleave gaps 56, 57 between the edges of the tongue and groove. Of coursethese gaps are exaggerated for purposes of illustration. In fact, theymay hardly be visible. However, it will not be the same net fit as ifthe dimple had been made before forming the tongues and recesses.Dimensions will be selected such that the dimple, when flattened, willcause sufficient movement to close this gap, and provide a tight fit,but it will not be as strong as the construction when the dimple isformed before the tongues and recesses are formed. Still, it is a usefulproduct, and the dimple can be formed either before or after the ring isformed. The drawing back of material referred to above can be minimizedor avoided by adding some bottom-thinning to the dimple-drawingoperation, thus further thinning and displacing material from thedimple's central area and thereby reducing or reversing the tendency todraw material away from the normal cut edge line of the tongue. Ofcourse, in every embodiment, the dimple is flattened only after the ringis formed and tongues and grooves are interengaged.

FIG. 9 shows a joint 60 where the tongues 61 and recesses 62 areseverely re-entrant, and have lobes 63. In such a construction acircular dimple 64 is most advantageous in all lobes, because it tendsto follow the edge of the tongue.

FIG. 10 shows a serpentine shaped joint 65 with tongues 66 and recesses67 that are generally rounded. Again, a circular dimple 68 is preferred,because it provides a dimple perimeter which generally follows the shapeof the tongue edge.

In fact, in all embodiments, the dimple shape is preferably selected sothat the dimple edge generally follows the tongue edge. This improvesthe edge interference when the dimple is flattened.

Product features characteristic of the two-stage out-of-plane/in-planereforming seam lock process include the existence on the surface of thefinished seam structure of not only the remains of the main depressionon the originally convex side of the dimple but also a slightlydepressed perimeter around the dimple area on its originally convexside. This distinctive depressed perimeter is the result of thereversals in stretching, bending and compression resulting from raisingand then compressively flattening the spherical or elongated dome-shapeddimples. These reversals in bending also provide the preferred jointedge rotation during flattening so that the originally concave dimpledside of the edge of the metal advances more forcefully into its sameside of the mating joint edge.

Use of this metal-rotation/edge bias feature makes it possible to add tothe friction a keyed-type of restraint against out-of-planedisplacements of the joint or seam. This can be done for example byopposing a seam's existing bias due to normal metal shear and/or jointassembly operations--this initial bias providing a preferred directionof joint out-of-plane disengagement which is then countered by theselected direction of rotation of the dimpled side of the seam. Or whereintrinsic bias due to shear or assembly is not significant, thiskey-lock effect can be achieved by providing multiple dimple lockstructures formed above and below the plane of the metal on one side ofthe seam, or formed on each side of the seam but on one side of themetal; in either case this achieves the positive edge-bias restraintsagainst out-of-plane displacements in either direction. In FIG. 10 toachieve the two way restraint against out-of-plane displacement downwarddimple 68 on one side of the seam cooperates with the upward dimple 69on the other side of the seam; and in the alternate arrangement depictedin FIG. 10, the dimple 70 cooperates with the dimple 71, both on thesame side of the seam.

It should be noted in FIG. 10 that seam 65 is not of the generallypreferred and stronger interlock-type geometry (which of course requiresspecial out-of-plane joint assembly techniques), but is interdigitatedand not locking. This indicates the applicability of this invention tonon-locking type tongue and groove structures. It also highlights thefact that the disclosed dimple-reform techinques to obtain interferenceengagements at the seam edge cannot only increase out-of-plane jointstrength, but can also add significantly to the pull strength of amechanical seam. In fact, multiple dimple arrangements such as shown inFIG. 10 generate in a non-locking joint interfacing or "stitch" typepositive restraints against pull separation comparable in effectivenessto a locking type joint geometry.

This invention is not limited by the thickness of metal, or to anyparticular shape or size of joint fingers--except, of course, that therelationship between metal thickness and the height, width, shape andlocation of the dimples must be selected so that the final flatteningoperation produces the desired edge displacements and seam interferenceengagements (as opposed to just buckling the dimple, or simply ironing adeformed tooth back into its basic tooth geometry without benefit of theinterference engagements at the seam).

In the techniques exemplified in FIGS. 5, 8 and 9, the dimple is shownas spaced from the edge of the tongue by an edge distance. The edgedistance is of course related to the size of the dimple and thethickness of the material. If it is too large, then the lateral forcewhich should be exerted at the edge may be lost in the material itself.Therefore the edge distance should not be too large. In fact, as shownin FIGS. 11 and 12, there need be no edge distance at all, although somewill usually be desirable in order to "smooth out" the effectimmediately at or near the tangent point.

Furthermore, it is possible for only part of a dimple to be provided, orfor a dimple to be disposed partly on one side, and partly on the otherside. In fact, it is possible, although not desirable, to provide onlypart of a dimple, and this on only one side.

In FIGS. 11 and 12, dimple 90 is formed in tongue 91, tangent to edge92.

In FIGS. 13 and 14, dimple 95 is formed in tongue 96 and recess 97,extending across edge 98, with a larger portion of it on tongue 96 thanon recess 97.

In FIGS. 15 and 16, dimple 100 is formed in tongue 101 and recess 102,across edge 103, the dimple being divided equally.

In FIGS. 11-16, it will be noted that in every case the dimple orportion of dimple is formed so that a downward pressure will exert notonly a rotational effect, but also a lateral force which tends to movethe edge laterally. Thus, the dimple is to be contrasted with a simplefold or bent tab, which is merely pressed flat. That does not exert alateral force. The dimple is a raised, not a purely bent, structure,which when flattened undergoes interference which tends to move thematerial laterally. A complete dimple is not necessary, but thearrangement is not merely the flattening of a fold. Thus, the term"dimple" is not limited to a structure whose periphery is completelywithin the plane of the material.

The terms "plane" and "in-plane" as used herein are, of course, relatedto the curvature of the cylinder. The seam can be, but usually is notflat, but has the curvature of the remainder of the cylinder, andaccordingly the terms are not strictly to be construed.

The term "interlocked" is not limited to structures in which the tonguesare re-entrant as in FIGS. 1 and 9, but includes those such as shown inFIG. 10 where the tongues and recesses can slide directly in and out.

This invention is not to be limited by the embodiments shown in thedrawings and described in the description, which are given by way ofexample and not of limitation but only in accordance with the scope ofthe appended claims.

We claim:
 1. A metal cylindrical ring having an axis, an inside surface,and an outside surface, said ring having been formed from a strip havinga tongue on one end of said strip and a recess on the other end of saidstrip, said tongue and recess being interlocked to form said ring withan in-plane seam, which seam comprises abutting edges of said tongue andrecess, at least part of which are thrust into an interference with oneanother by movement of metal, at least one of said edges against themetal of the other said edge, said ring having in its surfaces theshapes resulting from the of an out-of-plane dimple which when initiallyformed had a closed perimeter in said surfaces, and within saidperimeter a raised portion on one said surface, and a complementaryindented portion in the other said surface, followed by the flatteningof said dimple so that no portion of said dimple projects above eitherof said surface, said shapes lying close enough to said seam that saidmovement of metal to form said interference was formed at least in partby the flattening of said dimple.
 2. A metal cylindrical ring accordingto claim 1 in which said dimple was formed in the metal from which thestrip is made before the tongue and recess were formed.
 3. A metalcylinder according to claim 1 in which said dimple was formed in themetal from which the strip is made after the tongue and recess wereformed.
 4. A metal cylindrical ring according to claim 1 in which saidperimeter is contained entirely within said tongue.